2.7 Data analysis
To
develop a general pattern of ecosystem services in relation to plateau
pika disturbance across the five sites, two-way analysis of variance
(ANOVA) with a general linear model (GLM) was used to analyze the
effects of plateau pika disturbance, the sites and their interactions on
palatable plant biomass, plant species richness, soil water storage,
soil organic carbon, soil total nitrogen, soil total phosphorus and soil
total potassium stocks. In the model, the abovementioned parameters
acted as response variables, and plateau pika disturbance, site and
their interactions were introduced as fixed effects.
In addition, the paired-samples
T test was used to examine the
differences in
palatable
plant biomass, plant species richness, soil water storage, soil organic
carbon stock, soil total nitrogen stock, soil total phosphorus stock and
soil total potassium stock between the disturbed and undisturbed plots
at each site. Here, the “disturbed plots” and “undisturbed plots”
were regarded as one-to-one corresponding samples, the paired plots were
considered random factors, and the disturbed/undisturbed plots were
considered to be fixed effects, which were used to verify the results
from five sites and to support the general pattern.
To clarify the responses of
palatable plant biomass, plant
species richness, soil water storage, soil organic carbon stock, soil
total nitrogen stock, soil total phosphorus stock and soil total
potassium stock to the plateau pikas disturbance intensity, a linear
model (LM) was used to examine the relationships between palatable plant
biomass, plant species richness, soil water storage, soil organic carbon
stock, soil total nitrogen stock, soil total phosphorus stock and soil
total potassium stock and active burrow entrance densities in all
disturbed plots and in an individual site. The active burrow entrance
densities were considered to be a fixed factor, and they were used to
construct regression curves between palatable plant biomass, plant
species richness, soil water storage, soil organic carbon stock, soil
total nitrogen stock, soil total phosphorus stock and soil total
potassium stock and active burrow entrance densities.
Significant differences were
assessed at P <0.05. All statistical analyses were
performed with the SPSS 17.0 software package from SPSS Inc., Chicago,
IL, USA.